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Working principle of THK linear motion rail systems
- Jan 21, 2019 -

Working principle of THK linear motion rail systems


It can be understood as a kind of rolling guide, which is an infinite rolling cycle between the steel ball

 and the guide rail, so that the load platform can easily move linearly along the guide rail with high 

precision, and the friction coefficient is reduced to the conventional conventional sliding guide. One-

fifth of the time, it is easy to achieve high positioning accuracy. The design of the end block between 

the slider and the guide rail enables the linear guide to bear the load in all directions, such as up, 

down, left and right. The patented reflow system and the simplified structural design make the linear 

guide of HIWIN smoother and less noisy.


Slider - Turns the motion from a curve to a straight line. The new rail system allows the machine to 

achieve fast traverse speeds. At the same spindle speed, rapid traverse is a linear guide. Linear guides,

 like flat guides, have two basic components; one for the fixed component and the other for the 

moving component. Since linear guides are standard components, for machine tool builders. The only

 thing left to do is to machine the parallelism of the plane of the mounting rail and the alignment rail.

 Of course, in order to ensure the accuracy of the machine tool, a small amount of scraping of the bed

 or column is essential, and in most cases, the installation is relatively simple. The guide rail as a guide

 is hardened steel, which is finely ground and placed on the mounting plane. Compared with the

 planar guide rail, the geometry of the cross section of the linear guide is more complicated than that

 of the flat guide. The reason for the complexity is that the groove needs to be machined on the guide

 rail to facilitate the movement of the sliding element. The shape and number of the groove depend

 on the machine tool to be completed. The function. For example: a rail system that withstands both

 linear forces and subversive moments, compared to rails that only accept linear forces. The design is

 very different.


The basic function of the fixed element (rail) of the linear guide system is like a bearing ring, a bracket

 for mounting a steel ball, and the shape is a "v" shape. The bracket wraps around the top and sides of

 the rail. In order to support the working parts of the machine tool, a set of linear guides has at least

 four brackets. Used to support large work pieces, the number of brackets can be more than four.


When the working part of the machine tool moves, the steel ball circulates in the groove of the

 bracket, and the wear amount of the bracket is distributed to each steel ball, thereby extending the

 service life of the linear guide. In order to eliminate the gap between the bracket and the guide rail,

 the preloading can improve the stability of the rail system and obtain the preload. An oversized steel

 ball is placed between the rail and the bracket. The steel ball has a diameter tolerance of ±20 μm, and

 the steel balls are sorted and classified into 0.5 μm increments, and are respectively mounted on the

 guide rails. The magnitude of the preload is determined by the force acting on the steel balls. If the

 force acting on the steel ball is too large and the preloading time is too long, resulting in an increase

 in the kinematic resistance of the bracket, there will be a balance problem; in order to improve the

 sensitivity of the system and reduce the motion resistance, the preload is accordingly reduced. In

 order to improve the accuracy of motion and the accuracy of accuracy, it is required to have sufficient

 pre-added negative numbers, which is two aspects of contradiction.


When the working time is too long, the steel ball begins to wear, and the preload applied to the steel

 ball begins to weaken, resulting in a decrease in the movement accuracy of the working parts of the

 machine tool. If you want to maintain the initial accuracy, you must replace the rail bracket or even

 replace the rail. If the rail system is preloaded. The accuracy of the system has been lost, the only way

 is to replace the rolling elements.


The design of the rail system strives to maximize the contact area between the fixed component and

 the moving component. This not only improves the load carrying capacity of the system, but also the

 system can withstand the impact force generated by intermittent cutting or gravity cutting, spreading

 the force widely and expanding the bearing. The area of force. In order to achieve this, the groove

 system has a variety of groove shapes, two representative ones, one called Gothic (pointed arch), the

 shape is a semicircular extension, the contact point is the apex; the other It is a circular arc and can

 play the same role. Regardless of the type of construction, there is only one purpose, and it is

 intended to bring more rolling steel ball radii into contact with the guide rail (fixing element). The

 factor that determines the performance characteristics of the system is how the rolling elements

 come into contact with the rails, which is the key to the problem.